Influence of the trophic conditions in deep oceanic environments on the isotopic composition of live benthic foraminifera
The purpose of this thesis is to study the influence of the trophic conditions in deep oceanic environments on the isotopic composition of live benthic foraminifera, to improve their use as potential proxies of paléoproductivity. We studied three zones of the Northeast Atlantic Ocean : the Portugal...
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| Other Authors: | , , , |
| Format: | Doctoral or Postdoctoral Thesis |
| Language: | French |
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HAL CCSD
2007
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| Subjects: | |
| Online Access: | https://theses.hal.science/tel-00345812 https://theses.hal.science/tel-00345812v2/document https://theses.hal.science/tel-00345812v2/file/These_ClementineGRIVEAUD.pdf |
| Summary: | The purpose of this thesis is to study the influence of the trophic conditions in deep oceanic environments on the isotopic composition of live benthic foraminifera, to improve their use as potential proxies of paléoproductivity. We studied three zones of the Northeast Atlantic Ocean : the Portugal Margin (oligotrophic), the Bay of Biscay (meso-oligotrophic), and the upwelling zone off Cape Blanc (Mauritania, eutrophic). We established the major role of the organic flux and of the quality of the organic matter on the density, the bathymetric distibution and the microhabitats of foraminifers species. the superficial fauna react to the contributions of labile organic matter, while infaunal species depend on more refractory organic matter. Besides, we show the existence of a critical threshold of total organic matter flux of about 2gC/m²/year below which the development of the infauna is impossible. The study of the isotopic composition of some key species revealed that the offset in δ13C between a shallow infaunal species (e.g. Uvigerina peregrina) and a deep infaunal species (e.g. Globulimina spp.) can disciminate between a eutrophic environment (δ13C<0.5%) and an oligotrophic environment (δ13C>0.5%). Furthermore, in oligotrophic zones, we observed a gradual decrease of the delta δ13C according to the increasing organic matter flux, testifying of the direct influence of the latter on the composition or poral waters of the sediment. Le but de cette thèse est d'étudier l'influence des conditions trophiques en milieu océanique profond sur la composition isotopique de foraminifères benthiques vivants, afin d'améliorer leur utilisation en tant que proxies potentiels de paléoproductivité. Nous avons étudié trois zones de l'Atlantique Nord-Est : la Marge du Portugal (milieu oligotrophe), le Golfe de Gascogne (milieu méso-oligotrophe), et la zone à upwelling au large de Cap Blanc (Mauritanie, milieu eutrophe). Nous avons établi le rôle majeur du flux et de la qualité de la matière organique sur la densité, la ... |
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